5 LR is by far the best game of the series, gameplay is at its peak, massive character roster, lots of stages, game modes. The problem with it is the costume DLC many of which are impossible to get now, and the PC version has no lobbies which kills the game. But the gameplay itself is the best in the series. Dead or Alive perfected 3D fighting gameplay and avoided all the issues of modern Tekken (especially the boring repetitive combos that are just memorizing the same shit while the opponent floats in the air).
2,3 and 4 are all fantastic games but playing 5LR makes it hard to see them as anything but lesser.